1. Field of the Invention
The present invention relates to a variable-displacement vane pump, specifically to a variable-displacement vane pump used as a hydraulic pressure supply source for an automatic transmission.
2. Description of the Related Art
A conventional variable-displacement vane pump is disclosed in Japanese Patent Application Laying-open No. 62-276286. In this variable-displacement vane pump, a groove is provided over a semicircumference on the side surface of a cam ring, and both ends of the groove communicate with a suction-side containment portion and a discharge-side containment portion, respectively. This reduces an eccentric load exerted on the cam ring, and prevents occurrence of cavitation.
However, the above conventional variable-displacement vane pump has a problem in that the groove provided on the side surface of the cam ring tends to be clogged. Specifically, since this groove communicates with a hydraulic pressure passage at the inner peripheral surface side of the cam ring, debris being adhered in assembling, burrs peeled during operation the, and abrasion powder due to the vane rotation come into the groove. Such dust in the groove stays at a place in the groove where the average pressure is the lowest, that is, at the suction port side, and comes in between the side surface of the cam ring and a housing. As a result, seizing occurs on the side surface of the cam ring.